1. Field of the Invention
The present invention relates to a fuel cell system which is used in fuel cell-powered vehicles or the like, and more specifically to a fuel cell system which is provided with a means for purging an anode electrode side which is supplied with a fuel gas. Further, the present invention relates to a method of discharging a reaction gas from the fuel cell system.
Priority is claimed on Japanese Patent Application No. 2004-325120, filed Nov. 9, 2004, the content of which is incorporated herein by reference.
2. Description of the Related Art
In such a fuel cell mounted in a fuel cell-powered vehicle or the like, a fuel gas and a oxidizing agent gas are chemically reacted, and at the time of this reaction, energy is obtained and then directly channeled out to external circuits as electrical power. This type of fuel cell has a typical structure which includes an anode electrode and a cathode electrode, which together sandwich a solid polymer electrolyte membrane therebetween, in which a hydrogen gas as a fuel gas is supplied to the anode electrode side on one hand, and on the other hand, air containing oxygen as an oxidizing agent gas is supplied to the cathode electrode side.
Further, there is one type of fuel cell system, which uses such a fuel cell, and in which an unreacted fuel gas, which has passed through the anode electrode, is returned to an inlet side of the anode electrode to thereby promote the efficient use of the fuel gas. This fuel cell system is provided with a fuel gas circulating path, which connects an inlet side and an outlet side of the anode electrode and through which a fuel gas containing a reacted gas is repeatedly circulated, so that water (or moisture) and other impurities are gradually and increasingly deposited in a path (including a circulating path portion) at the outlet side of the anode electrode. Consequently, a mechanism for appropriately purging an internal gas is provided on the path at the outlet side of the anode electrode.
In a fuel cell system of this type, when operation of a fuel cell is stopped, it is necessary to reliably discharge water and the like, which remain in an outlet side of the anode electrode, to outside in order to avoid freezing and clogging in a path at a time of resumption of operation. As a countermeasure, a new type of fuel cell system has been developed, wherein a dilution gas that is different from a fuel gas is introduced in the anode electrode side and wherein water and other impurities in a path are purged by this dilution gas (see, for example, Japanese Unexamined Patent Application, First Publication No. 2003-331893).
This fuel cell system is structured such that a feed path for an oxidizing agent gas is connected to the anode electrode side and that a gas feed valve of open/close type is provided on the feed path and is opened at a time of purging of the anode electrode side. It is also structured such that a plurality of discharge ports are provided at an outlet side of the anode electrode and that these ports are opened at a time of purging to thereby discharge residual gas of the anode electrode side together with a dilution gas (oxidizing agent gas) to outside.
However, in this conventional fuel cell system, since all of the discharge ports are suddenly opened at a time of purging of the anode electrode side, a fuel gas emission concentration of a discharged gas is temporarily and totally raised.
Therefore, in the above-described conventional fuel cell system, provision is made in which power generation is continued within a predetermined period of time while continuing stoppage of the supply of a fuel gas and in which purging is carried out after a fuel gas in a fuel gas circulating path has sufficiently been consumed. As a result, in this conventional fuel cell system, time required for the completion of purging is inevitably elongated. Therefore, at the present time, improvements with respect thereto are earnestly desired.